Obesity is the most obesity which are present prior to the onset of excess weight gain has been problematic. Recently, it has been shown that the timing of body mass index (BMI) rebound may be a predictor of future obesity. BMI increases during the first year of life. It then declines until it reaches a minimum value during childhood and subsequently increases into adolescence and adulthood. The nadir of BMI is called BMI rebound. Studies have shown that BMI rebound at a younger age is associated with increased risk of obesity later in life. Currently, very little is known about the epidemiology of BMI rebound. The purpose of the proposed investigation is to precisely determine the age of BMI rebound and evaluate the body composition changes which occur during this time to determine if BMI rebound corresponds to a rebound in adiposity. In addition, determinants of the changes in body composition, such as diet and physical activity, will be investigated. Finally, the relationship of the timing of BMI rebound to body composition and cardiovascular risk factor status will be studied. The proposed investigation is a cohort study designed to follow 320 children from age three age seven years. Subjects will be evaluated every four months during the period of the study. Data will be collected on height, weight, body composition, diet and physical activity. At age seven years, the level of adiposity, the distribution of body fat, and cardiovascular risk factors will be studied. The investigators note that better understanding of the epidemiology of BMI rebound could lead to improved identification of children at high risk of future obesity prior to excess weight gain. They further note that elucidation of the determinants of the timing of BMI rebound could lead to the development of clinical and public health strategies to prevent the development of obesity.